Field of the Invention
The present invention relates to an image forming apparatus which includes a developing device equipped with a plurality of developer bearing members which bears a developer for developing an electrostatic latent image on an image bearing member.
Description of the Related Art
Conventionally, in a copying machine using an electrophotographic system, a laser beam printer, a facsimile machine, and an image forming apparatus such as a printing apparatus, the surface of an image bearing member is evenly charged, an image is exposed by a semiconductor laser or an LED, and an electrostatic latent image is formed on the image bearing member. Then, after the electrostatic latent image is visualized as a developer image by a developing device, the visible image (the developer image) is transferred onto a transfer material, and the transferred visible image is fixed to the transfer material by a fixing apparatus and output.
In recent years, high speed and high quality have been strongly requested for the image forming apparatus. As a developing device used in the image forming apparatus capable of making a high-speed output, there is a configuration which includes a plurality of developer bearing members for bearing the developer.
Since the developer can be supplied to the electrostatic latent image on the image bearing member any number of times using the plurality of developer bearing members, an appropriate density can be kept even when the operation is increased in speed. In addition, since the toner attached to the image bearing member by the developer bearing member on the upstream side in the rotation direction of the image bearing member is once peeled off by the developer bearing member disposed on the downstream side in the rotation direction and is attached again, it is possible to obtain an image more faithful to the latent image.
As a way of disposing the plurality of developer bearing members, as disclosed in Japanese Patent Laid-Open No. 2011-191664 or Japanese Patent Laid-Open No. 2004-29569, a configuration that the plurality of developer bearing members abuts in a short distance, and a configuration that the developer bearing members are disposed in a separated distance.
In Japanese Patent Laid-Open No. 2011-191664, the plurality of developer bearing members is disposed to be separated from each other, and a regulating member is provided to regulate the developer on each developer bearing member. However, the configuration that the developer bearing members are disposed to abut can be made simple compared to the configuration that the developer bearing members are disposed to be separated, and can be made in small size so that the configuration is received a lot of attention in recent years.
In the configuration that the developer bearing members are disposed to abut, the developer bearing members on the downstream side except the developer bearing member on the most upstream side are disposed with a gap with respect to one developer bearing member on the upstream side in a non-contact manner, and the developer on the developer bearing member is regulated by the gap. The developer amount on the developer bearing member can be adjusted by adjusting the gap between the developer bearing members (see Japanese Patent Laid-Open No. 2004-29569). With such a configuration, it is possible to achieve high speed and high quality by a simply configuration.
However, in the configuration disclosed in Japanese Patent Laid-Open No. 2004-29569, in a case where the apparatus is downsized, an agglomerate is accumulated between the developer bearing members which perform the regulation of the developer. Therefore, there occurs a phenomenon of inhibiting a coat layer of the developer on the developer bearing member. When an image is formed in such a circumstance that the coat layer of the developer bearing member is inhibited, an image defect such as a vertical streak in half tone is generated. In addition, a surface property of the developer bearing member is changed depending on an external temperature/humidity circumference. Therefore, a trace may be generated in the developer bearing member.